def f(n):
    for i in range(2,n):
        if n%i==0:  return False
    return True

cif=['zero','two','three','four','five','six','seven','eight','nine']
left=[]
right=[]
s=input()
a=s.split()
b=''
for x in a:
    b+=str(cif.index(x))
b = int(b)
for c in range(b, 1015):
    if f(c):
        right.append(c)
for c in range(2, b):
    if f(c):
        left.append(c)


if b - max(left) <= b - min(right):
    print(max(left))
else:
    print(min(right))